The present invention relates to an electrophotographic photosensitive member used for a image forming apparatus such as copy machine, electrostatic printing, facsimile, laser printer and electrostatic recording, a preparation method thereof, an image forming process, an apparatus and a process cartridge using the electrophotographic photosensitive member. More specifically the present invention relates to an electrophotographic photosensitive member used for an image forming apparatus, a preparation method thereof, an image forming apparatus which is capable of forming high quality of images with high speed operation for a long period of repeated use time.
There are corona charging method and contact charging method used in electrophotograpy, those both have been used as electric charging method to make the photosensitive member electrically charged. The corona charging method contains corotron charging method and scotron charging method having a grid, those are a method in which AC potential or DC-overlapped AC potential is applied to the charging wire such as tungsten wire or nickel wire and so forth which being stretched on the central position of a housing shielded by metal plate, thereby corona discharge is induced which makes electrically charged photosensitive member.
However in this kind of method a high voltage is applied to the charging wire thus occurs ozone and nitrogen oxides products. And it has been known that such oxidant products affect bad influences upon, not only environmental aspect, but also the photosensitive member from the viewpoint of their durability and characteristics of produced image.
In recent years, instead of above described method using the charging wire for corona discharging, the contact charging method has been used in practice for the purpose of obtaining a lowered or an eliminated generation of ozone and a lowered consumption of electric power. The contact charging method is a method in which AC potential or DC-overlapped AC potential is applied to a charging member having electric resistance from 102 to 1010 xcexa9xc2x7cm degree, which is pressed to contact with the surface of an electrophotographic photosensitive member, thereby the electrophotographic photosensitive member is electrically charged. This charging method, which is subjected Paschen""s law, is effectuated by a discharge emitted from the charging member toward the photosensitive member as charge-receiving member, therefore the charging of the photosensitive member is initiated by applying electric potential more than threshold level of voltage. In the execution of the contact charging method, an electric potential level to be applied may be lowered in comparison with that of corona charging method, but the method accompanies with an inevitable discharging, thus generates small amount of ozone and nitrogen oxides.
And the contact charging method causes a contact of charging member with the surface of the electrophotographic photosensitive member (hereinafter may also be referred as photoreceptor), therefore there is a problem that the abrasion of the surface of the electrophotographic photosensitive member is increased.
In the field of electrophotographic apparatus the demands such as higher quality image reproduction, higher tolerance, lower running cost and full-color imaging have been growing large in market in recent years. Particularly a full-color duplication has been popularized by the commercial diffusion of color printer and color copier, thus a demand for duplicating full-color image with almost same high speed as that of mono-color printing has growing. For satisfying this demand an attention has been paid to so called tandem type of full-color image forming apparatus. The tandem type of full-color image forming apparatus includes a plurality of photosensitive members arranged in parallel and equipped with developing unit respectively, and respective single colors formed on each photosensitive member are transferred and overlaid one by one onto the surface of recording member to make composed color image. This tandem type of full-color image forming apparatus is capable of significant time saving for printing action, in comparison with that of so called one drum type of image forming apparatus which employs only one photosensitive member and thereon are repeated a plurality of image forming actions (usually four times of action) to form full-color image. However such tandem type of full-color image forming apparatus has a plurality of image forming sections independent each other, therefore becomes large in apparatus scale, thus is apt to be expensive.
At the present time, with a demand for obtaining high quality of color image by color printer or color copier, as light sources for such photo-printers, the application of laser diodes (LDs) and light emitting diodes (LEDs) both which have smaller light beam diameter capable of high power emission so as to make itself capable of a finer dot recording has been prevailingly be trended in the field of image forming apparatus. Meantime, thicker CTL (charge transfer layer) of photosensitive member causes more decreased straight passages in the CTL for electric charges which are injected into the CTL and arrive to the surface of the CTL to neutralize the surface charges having opposite polarity, hence occurs blurring of images formed, therefore it is required to shorten the thickness of CTL.
Generally speaking, in Carlson process, the CTL is abraded and decreases its thickness by its repeated uses. Accordingly, for the purposes of avoiding the generation of smearing in back ground area of printed image or avoiding the decrease of the image density which are caused by decrease in electric charge potential and decrease in photosensitivity of the photosensitive member, it is thought to shorten the thickness of the CTL, but such shortening of the CTL thickness was disadvantageous from the point of view to attain high durability of the photosensitive member.
There is a tendency to require a higher sensitivity and a higher responsibility of the photosensitive member in accompanying with an achievement of high speed electrophotographic apparatus, a smaller photosensitive member in accompanying with an achievement of down sized apparatus, thus requiring a higher tolerance of the photosensitive member. For such requirements Japanese patent No 2838891 considered the quantum efficiency in dependence on the strength of electric field in photosensitive member, and discloses a photosensitive member which is achieved a high sensitivity, compatible with an improved durability, by the combination of a CTL having relatively large value of 25 to 60 xcexcm in thickness and a CGL (charge generating layer) having quantum efficiency depended slightly upon the strength of electric field. However there was a shown drawback with this photosensitive member that it reveals the decease in sensitivity pursuant to the decrease in thickness of CTL caused by abrasions of the layer in the photosensitive member used repeatedly.
Hereupon, an electrophotographic photosensitive member has been designed and used in real which has an improved anti-abrasion nature by providing a protection layer on the photosensitive layer.
For instances Japanese Patent Laid-open Publication of Tokkai Shou 63-91666 discloses a technique to provide a protection layer made of silicone material on the photosensitive layer, Japanese Patent Laid-open Publication of Tokkai Hei 03-155558 discloses a technique to provide a protection layer made of curable silicone resin, Japanese Patent Laid-open Publication of Tokkai Shou 60-3639 discloses a technique to make a protection layer made of a composed mixture of a curable resin and an acrylic resin, Japanese Patent Laid-open Publication of Tokkai Shou 57-176057 discloses a technique to provide an insulate protection layer made of a fluoride resin dispersing therein powder of hard particles onto the photosensitive layer, Japanese Patent Laid-open Publication of Tokkai Shou 63-18354 discloses a technique to provide a protection layer containing anti-oxidant, and Japanese Patent Laid-open Publication of Tokkai Hei 01-205171 discloses a technique to improve the tolerance of the most upper layer by incorporating therein an inorganic filler of particles.
However, it is known that in such kind of photosensitive members, which have an improved anti-abrasion nature, occur an adhesion of products produced in discharging course to the surface of photosensitive member, and it becomes small in the electric resistance of the surface of photosensitive member. But the removal by abrasion of the outermost surface thin layer materials having been decreased in electric resistance is not conducted because of its strong anti-abrasion nature, and eventually electrostatic charge is not held on the surface, hence occurs phenomena such as image drifting and image blurring.
Therefore, in conventional electrophotographic photosensitive member which has been given an improved anti-abrasion nature by the protection layer containing filler, the prevention of image blur has been executed by slightly abrading the surface of protection layer by controlling filler amount to be contained in the protection layer. In such constitution of the photosensitive member, to make abrading of the protection layer even very scarce degree of abrasion, the protection layer must be formed with a certain thickness, but thickened protection layer is apt to conduct side effects such as an elevated electric potential at lightening exposed area and so forth.
With regard to copy machines commercially available, there is a copy machine which carries on a photosensitive member having prolonged life time capable of 1000 kilo running. Actually in this copy machine a drum heater is inserted in the inside space in hollow configuration of photosensitive member, for preventing a generation of image blur, therefore is unavoidable from the use of complexion and enlarged diameter of thus considerably expensive photosensitive member. Further it is a energy consumable due to the heater. By these reasons, the photosensitive member having a protection layer on its surface and heater in its inside is difficult to use for the tandem type of image forming apparatus, therefore implementation thereof is not yet realized until now.
It is desirable to give a comparatively thin layer thickness in the protection layer, because side effects such as elevation of electric potential at lightening exposed area and so forth are suffered from the accumulation of electric charges. As a mater of course, anti-abrasion nature that is hard to abrade for a long period of repeated operation time is required. On the other hand, photosensitive member having such improved anti-abrasion nature occurs adhesion of products produced during discharging course thus results decreasing of electric resistance at surface of the photosensitive member, the abrasive removal of the outermost surface thin layer material having thus been decreased in electric resistance is however not conducted because of its strong anti-abrasion nature, and eventually electrostatic charge is not held on the surface, hence occurs phenomena such as image drifting and image blurring. By these reason, it has been difficult to implement photosensitive member which having protection layer hardly abraded and having hardly occurring image blurring even if without use of auxiliary apparatus such as drum heater and the like.
It is therefore an object of the present invention to provide an electrophotographic photosensitive member having high durability capable of stable image productions for a long period of utilizable time.
It is another object of the present invention to provide a coating liquid for forming a protection layer for the electrophotographic photosensitive member, and a production method of the electrophotographic photosensitive member.
It is still another object of the present invention to provide an image forming process using the electrophotographic photosensitive member.
It is still another object of the present invention to provide an image forming apparatus using the electrophotographic photosensitive member.
It is still another object of the present invention to provide a process cartridge using the electrophotographic photosensitive member.
Having been focussed to the above described objects with regard to protection layer which has to be a strong anti-abrasion nature and show no blurring in images for long period of operation time, serial concentrated studies have been strenuously conducted for the purpose of solving above described problems which were belonged to conventional techniques.
And as a result, it is found out that significant improvements that an excellent anti-abrasion nature is shown, excellent images are reproduced for long period of running time with no or hardly generated image blurring are achieved by employing; an electrophotographic photosensitive member having a photosensitive layer provided on an electroconductive supporting body and a protection layer provided on the photosensitive layer, wherein the protection layer comprising at least finely divided particles of metal oxide, an organic acid and a binder resin, the binder resin is a thermo-curable resin, the organic acid being contained an amount of 0.05 wt. % to 5 wt. % for the amount of the thermo-curable resinwherein the protection layer comprising at least finely divided particles of metal oxide, an organic acid, and a binder resin, the binder resin is a thermo-curable resin, the organic acid contained is contained an amount of 0.05 wt. % to 5 wt. % for the amount of the thermo-curable resin.
It has been known that for example in case of poly carbonate resin, which has a comparatively high hardness among various thermoplastic resins, is used as binder resin for the protection layer, if high strength is given to the poly carbonate resin so as to make it causing no or only scarce abrasion, image blur takes place. It is though that this phenomenon is caused by a mechanism that there are existing a number of poly carbonate bonding sites in the poly carbonate resin, therefore products in discharging are absorbed to the bonding sites, and absorbents are gradually accumulated thereby surface electric resistance is dropped hence charges arc not held.
In contrast to this, with a photosensitive member having a protection layer by the present invention, no or very low blur is generated in spite of very low abrasion with the photosensitive member surface. The reason for the phenomenon is not clear yet, but following issues may be thought at the present moment.
In case of that the surface of photosensitive member is abraded by contacts with contacting members such as recording member instanced as paper sheet and so forth, cleaning member instanced as counter blade, the electrophotographic photosensitive member used in the present invention includes finely divided particles of metal oxide, therefore above described contacting members contact with not only resin materials used in the protection layer but also the metal oxide particles contained in the protection layer. Here, the metal oxide particles have enough hardness, and hardly abraded, in comparison with above described contacting members which basically consisting of aggregated moleculars and are govern by mainly Van der Waars bondings acting as inter-moleculars bonds, therefore can prevent or suppress the abrasion of resin part of protection layer, hence improving anti-abrasion nature.
And, the binder resin of the protection layer in the present invention is made by heat curing of curable resin, therefore cross-linking reaction between resin moleculars makes combined each resin material.
In general, cross-linking reactions in curable resins are irreversible reactions, thus number of radical groups is decreased with the progress of bonding reaction between the radical groups. As already described above, the products produced in discharging are absorbed to the bonding sites. In case of absorbing the products produced in discharging onto the surface of electrophotographic photosensitive member, it is thougth that more existence of radical group leads to easier absorption of the products in discharging onto the surface of the photosensitive member, and absorbed products become difficult to remove the surface.
It is thought on the contrary that, the electrophotographic photosensitive member of the present has smaller number of radical groups at the surface, therefore is afraid to absorb the products in discharging to the surface of the photosensitive member, as a result, deposition of the products in discharging to the surface of the photosensitive member is suppressed, and if any deposition is brought with the products, the deposited products are endowed with weak adhesion strength thus can be removed easy, accordingly the decrease of an electric resistance is difficult in case of the electrophotographic photosensitive member of the present.
And, in the present invention an organic acid is contained in the protective layer. This acid works as a catalyst at cross-linking reaction of resin, and by this acid, cross-linking reaction of resin is fully progressed at relatively low temperature in relatively short time, thus existence of residual reactive radical groups can suppress in fewer level, than that of the reaction system containing no organic acid. The existence of residual reactive radical groups are possible sites for absorbing the products produced in discharging, thereby decreasing of the electric resistance is likely to cause an image blur. And the existence of residual reactive radical groups, with the time lapse, may be changed to charge traps in a forbidden energy level of the electrophotographic photosensitive member, acting as elements inducing an electric potential rising of light-exposed area in the electrophotographic photosensitive member.
The use of organic acid as a hardening agent for curable resin, as such technique itself has been known in the art of electrophotographic photosensitive member. For instances Japanese Patent Laid-open Publication of Tokkai Hei 06-266142 discloses a technique to use organic acid such as prenic acid anhydride, pyromellitic acid anhydride, trimellitic acid anhydride as a hardening agent to make cure the epoxy resin used for protection layer of electrophotographic photosensitive member, Japanese Examined Patent Publication of Tokkou Hei 06-90539 discloses a technique to use inorganic acid, organic acid or amine as a hardening agent for protection layer consisting of a mixture resin of curable silicone resin and acrylic resin containing therein finely divided particles of tin oxide, titanium dioxide, indium oxide, antimony oxide and the like having diameter of 10 nm to 20 nm.
However, the amounts of inorganic acid, organic acid or amine as a hardening agent added in protection layer are no more than catalystic amount in conventional techniques. It was an anxiety of the skilled in the art that the use of excess amount of the catalyst also may result the existence of residual hardening catalyst which was also apt to be active sites capable of absorbing the products produced in discharging, acting as elements inducing an electric potential rising of light-exposed area in the electrophotographic photosensitive member, thereby decreasing of the electric resistance was likely to cause an image blur. Accordingly the avoidance for such addition of excess acid into the protection layer might be a normal sense.
Rising of electric potential in exposed area by light emission causes an irregular image, therefore it has been thought that hardening condition likely to remain the reactive radical groups after completion of the hardening reaction is unfavorable. For the purpose of accelerating the hardening reaction with suppressing the residual reactive radical group under the condition of no existence organic acid, longer reaction time and higher reaction temperature are required, however if larger amount thermo-energy is imposed, there may be brought drawbacks that the photosensitive member does not show a necessary sensitivity for emitted light and so forth, due to changes of charge transfer material and charge generation material. And if not any change, there is required much more energy to make harden the used resin, hence environmental load becomes larger thus unfavorable.
By the way, if a protective layer including fine particles of metal oxide is overlaid on a CTL, there is a possibility of accumulation of the remained charges in course of repeated uses of the photosensitive member, and thereby the rising of electric potential at exposed area by light emission is induced. It is thought that the inter surfaces between metal oxide fine particles, between metal oxide fine particle and resin material, between them and charge transfer material acts as traps for the charges, which impede the smooth immigration of the charges.
In this case, it is thought to suppress such charges accumulation of the residual charges, by increasing the amount of charge transfer material included, however it is worried that larger ratio of the contained charge transfer material causes more decreased anti-abrasion nature. And in generally speaking, the charge transfer material may be expensive, hence conducts a cost escalation of the produced photosensitive member.
As compared with above described technique, an amount of the contained organic acid for the amount of used resin in the present invention is in the range of 0.05 wt. % to 5 wt. %. And it is thought that the organic acid in the present invention is used as not only catalyst, but also it acts as Lewis acid in the protection layer to cooperate with the charge transfer material which in almost all case shows a basic characteristic nature, pursuant to its aromatic poly-ring structure, and it acts as an agent for mitigating the relaxation state in the binder polymer material composing protection layer, to decrease the permeability of ozone, nitrogen oxide, water vapor and so forth. Accordingly in taking consideration of a balancing between the catalystic effect and the effects of Lewis acid and the polymer conformation-shrinkage effect, favorable amount of the organic acid is in the range of 0.1 wt. % to 3 wt. %.
Namely, the organic acid acts as a catalyst in the course of curing of the binder resin, and thereafter is remained in the protection layer to decrease the bulk resistance of the protection layer, and to release the latent heat which impedes the electric conductivity. In this situation, it is thought that the organic acid in the present invention is excellent in compatibility with the resin, therefore does not localizes, thus exhibits an effect to reduce the electric resistance properly over the whole span. In this case if inorganic acid is used as an acid, it is apprehensive that the inorganic acid is inferior in compatibility with the resin thus localizes in the protective layer at an occasion of it being left in the protection layer. If the acid localizes in the protection layer, in that local sites, an extreme reduction of the electric resistance are induced, thereby initial and dark (not exposed by light) electric potential are reduced in that spots, thus they cause irregular image such as black spots and the like. On the other hand, in the preparation of a coating liquid for forming the protection layer, organic solvents are used in almost cases in due consideration of solubility of resin and charge transfer material, on such occasions use of inorganic acid is poor solubility for the organic solvents, therefore is unfavorable from the viewpoint of the stability of coating liquid.
Further, by the present invention, an electrophotographic photosinsitive member characterized by using aromatic sulfonic acid or derivatives thereof. It becomes now clear in the present invention that the aromatic sulfonic acid or derivatives thereof show a strong acidity and a high effect as of catalyst, therefore hardening reaction of the resin may get off by a small energy, thus causing large effects in the energy saving and lowering the environmental load, and the sulfonic acid has an excellent solubility in the organic solvents, therefore is satisfactory in the stability of the coating liquid, the workability in course of forming the protection layer, and so forth. Further, it shows a good compatibility with resin, accordingly is difficult to generate above described black spots.
And, the electrophotographic photosensitive member used in the present invention can suppress an image drifting without heating by drum heater and the like, therefore the installation of the drum heater at the inside space of or closed to the electrophotographic photosensitive member loaded on image forming apparatus, thus is effective for down sizing of the image forming apparatus and for the energy saving purpose. Further the lay out of wiring and mechanism regarding with the heater can be eliminated, that is effective for the simplification of image forming apparatus, hence a reduction of the cost and a save of energy can realized.
As described hereto, according to the present invention, there is a provided an electrophotographic photosensitive member having a photosensitive layer provided on an electroconductive supporting substrate and a protection layer provided on the photosensitive layer, wherein the protection layer comprising at least finely divided particles of metal oxide, an organic acid, and a binder resin, the binder resin is a thermo-curable resin, the organic acid contained is contained an amount of 0.05 wt. % to 5 wt. % for the amount of the thermo-urable resin. Here, in case of an included amount of organic acid less than 0.05 wt. % for the amount of resin, even if the action as a catalyst may achieve, there is a possibility that the effect for suppressing above described elevation of residual electric potential becomes smaller, therefore the effect to suppress increases of electric potential at light exposed area by repeated uses. And in case of an included amount of organic acid more than 5 wt. % for the amount of resin, there is a possibility that the bulk electric resistance becomes too much smaller, thus electrostasic charge being charged on the surface of the photosensitive member is not held, hence may occur image drifting and smear at back ground area, thus is unfavorable. In particularly under the condition of high temperature and high humidity such tendency becomes significant.
And, according to the present invention, An electrophotographic photosensitive member of above described type having a photosensitive layer provided on an electroconductive supporting substrate and a protection layer provided on the photosensitive layer, wherein the protection layer comprising a charge transfer material is provided. By such inclusion of a charge transfer material into the protection layer, the electrophotographic photosensitive member showing a reduced residual electric potential and a reduced delay of rising up time in electric charging is implemented.
The ratio by weight of binder resin and the charge transfer material in the protection layer is favorable to be in the range of 3/1 to 1/3. In case of the ratio less than 3/1, there is a possibility that the charges can not migrate smoothly in the protection layer, therefore the effect to suppress the residual electric potential becomes insufficient. On the other hand, in case of the ratio more than 1/2, there is the possibilities that the hardening of resin in the protection layer is impeded, and the charge transfer material is crystallized out to the protection layer, those cause a reduction of anti-abrasion nature of the protection layer or an inferiority of image reproduced. In case of the ratio in the range of 3/1 to 1/3, the charges can migrate smoothly in the protection layer, the effect to suppress the residual electric potential becomes sufficient enough. And, a reduction of anti-abrasion nature of the protection layer and an inferiority of image can prevented, with no impedance of hardening of resin in the protection layer and nor crystallizing out of the charge transfer material.
By the present invention, the curable resin of the protection layer constitutes from a thermo-curable acrylic resin, a melamine resin, a benzo-quanamine resin, thereby an electrophotographic photosensitive member, which has a sufficient anti-abrasion nature, an excellent electrostatic property, and a lowered production cost, can be realized.
Namely, a favorable mode of the present invention concerns with an electrophotographic photosensitive member having a protection layer formed by heating to cure above described thermo-curable acrylic resin, and a melamine resin and/or a benzo-quanamine resin.
The electrophotographic photosensitive member having a protection layer formed by heating to cure a thermo-curable acrylic resin, and a melamine resin and/or a benzo-quanamine resin so as to make a three dimensional network structure by cross-linking reaction, and the protection layer is excellent in film-forming characteristic thus can form a smooth surface, has a sufficient anti-abrasion nature and a excellent electrostatic, property, and can be produced by a reduced cost. And the compatibility of the thermo-curable acrylic resin, with the melamine resin and/or the benzo-quanamine resin is very good, therefore a protection layer showing high transparency can be formed.
Among those materials, at least one material is favorable to be the thermo-curable acrylic resin.
And at least one material other than the thermo-curable acrylic resin in those materials is favorable to be the melamine resin or the benzo-quanamine resin.
Further, the present invention includes a favorable mode in which the ratio by weight of the thermo-curable acrylic resin, and the melamine resin or/and the benzo-quanamine resin is in the range of 9/1 to 4/6.
Pursuant to experiments, excellent results were shown in the durability for abrasion and the dispersion stability of the metal oxide,and the hardness of the hardened resin and so forth, in case of the ratio by weight of the thermo-curable acrylic resin, and the melamine resin or/and the benzo-quanamine resin was in the range of 9/1 to 4/6.
Further, the electrophotographic photosensitive member of the present invention, as described above, is a photosensitive member which is decreased in the permeability of hazard gas such as ozone, nitrogen oxides, water steam and so forth. The protection layer thereof is favorable to have a permeability less than or equal to 50 mgxe2x80x942 daysxe2x88x921xe2x88x921.
Furthermore, as already described above, the electrophoyographic photosensitive member used in the present invention can suppress the image drifting without heating by drum heater and the like, therefore the installation of the drum heater at the inside space of or closed to the electrophotographic photosensitive member loaded on image forming apparatus, thus is effective for down sizing of the image forming apparatus and for the energy saving purpose. Further the lay out of wiring and mechanism regarding with the heater can be eliminated, that is effective for the simplification of image forming apparatus, hence a reduction of the cost and a save of energy can realized.
Such kind of the electrophotographic photosensitive member of the present invention is, not essential, but favorable to be a laminated type of photosensitive member which has an ognanic photosensitive layer consisting of a CGL and a CTL over laid one by one. A function-sharing type of photosensitive layer in which charge generation function is separated from charge transfer function is prepared by constituting the photosensitive layer with a CGL and a CTL over laid one by one,
And in such kind of the electrophotographic photosensitive member of the present invention can be an electrophotographic photosensitive member having an under coated layer between an electrophotoconductive supporting substrate and the photosensitive layer. By providing the under coated layer, improvements such as an improvement of adhesive property, prevention of moire, an improvement of coating operation, reduction of residual electric potential can be designed.
Further, by the present invention, there is provided a coating liquid used for forming the protection layer of the electrophotographic photosensitive member, which consists of a binder resin including a curable resin, a fine powder consisting of metal oxides particles, an acid catalyst, a charge transfer material which being added if necessary, wherein the solid content is in a range from 0.5 to 30 weight % for the total coating liquid.
Further, by the present invention, there is provided a preparation method of an electrophotographic photosensitive member comprising steps of applying a coating liquid used for forming the protection layer of the electrophotographic photosensitive member by spraying the coating liquid onto a photosensitive layer, then heat-setting it to form the protection layer, wherein the coating liquid is a coating liquid used for forming the protection layer of the electrophotographic photosensitive member, which consists of a binder resin including a curable resin, a fine powder consisting of metal oxides particles, an acid catalyst, a charge transfer material which being added if necessary, and the solid content is in a range from 0.5 to 30 weight % for the total coating liquid.
Further, by the present invention, there is provided an image forming process comprising at least steps being repeatedly conducted of latent image forming step for forming an electric latent image upon the aforementioned electrophotographic photosensitive member, developing step for developing the latent image to make a toner image, toner image transfer step for transfer the toner image onto a image receiving medium.
The image forming process shown an excellent anti-abrasion nature of the surface of the photosensitive member, thus excellent images are reproduced for long period of running time with no or hardly generated image blurring.
Further, by the present invention, there is provided an image forming process according to the aforementioned image forming process, wherein the latent image forming step for forming an electric latent image upon the aforementioned electrophotographic photosensitive member is a latent image forming step comprises steps of a charging step for electrically charging the aforementioned electrophotographic photosensitive member, and an exposing step for exposing the electrophotographic photosensitive member in image wisely by exposing with a light irradiation of image shape or with an emission of the light beam.
It is possible to directly give the electric latent image onto the electrophotographic photosensitive member by using a special electrode, however for demonstrating the excellent property of the electrophotographic photosensitive member, the latent image forming procedure using the exposure with a light irradiation of image shape or with an emission of the light beam are advantageous.
Further, by the present invention, there is provided an image forming apparatus equipped with an electrophotographic photosensitive member having a photosensitive layer provided on an electrically conductive supporting substrate and a protection layer provided on the photosensitive layer, a latent image forming apparatus for forming an electrostatic latent image on the surface of the electrophotographic photosensitive member, a developing apparatus for developing the electrostatic latent image, wherein the protection layer comprising at least finely divided particles of metal oxide, an organic acid and a binder resin, the binder resin is a thermo-setting resin, the organic acid being contained an amount of 0.05 wt. % to 5 wt. % for the amount of the thermo-setting resin.
The image forming apparatus shown an excellent anti-abrasion nature of the surface of the photosensitive member, thus excellent images are reproduced for long period of running time.
Further, by the present invention, there is provided an image forming apparatus having a plurality of image forming units, and each image forming unit equipped with respectively an electrophotographic photosensitive member having a photosensitive layer provided on an electric conductive supporting substrate and a protection layer provided on the photosensitive layer, a latent image forming apparatus for forming an electrostatic latent image on the surface of the electrophotographic photosensitive member, a developing apparatus for developing the electrostatic latent image to make a toner image, a toner image-transfer unit for transfer the toner image, and the image forming apparatus having a toner image-receiving mean which is suffered from the transfers of each toner images on the surface thereof, a driving mean for driving the toner image-receiving mean so as to move the surface of the toner image-receiving mean to sequentially face the surface thercof to the each surface of respective electrophotographic photosensitive member, wherein the protection layer comprising at least finely divided particles of metal oxide, an organic acid and a binder resin, the binder resin is a thermo-setting resin, the organic acid being contained an amount of 0.05 wt. % to 5 wt. % for the amount of the thermo-setting resin.
The image forming apparatus shown an excellent anti-abrasion nature of the surface of the photosensitive member, thus excellent images are reproduced for long period of running time with no or hardly generated image blurring, if spite of equipped with no drum heater.
Further, by the present invention, there is provided an image forming apparatus according to aforementioned image forming apparatus, wherein the latent image forming apparatus is a latent image forming apparatus having an electric charging member contacted with (contact type of charger) or adjacent to (adjacent type of charger) the electrophotographic photosensitive member.
In this image forming apparatus, by the electric charging member contacting with or placing close to the electrophotographic photosensitive member, the generations of ozone, nitrogen oxides and the like can be dccreased. And the electrophotograghic photosensitive member used for such kind of image forming apparatus becomes excellent in anti-abrasion nature, therefore if the electric charging member is used in a contacted state with the electrophotograghic photosensitive member, the suface abrasion of the the electrophotograghic photosensitive member can be suppressed in a small degree.
Further, pursuant to the present invention, there is provided an image forming apparatus according to aforementioned image forming apparatus, wherein the toner imagc-receiving mean is an intermediate transfer medium, toner images developed on the plurality of electorophotographic photosensitive members are firstly transferred to form over-laid images on the intermediate transfer medium one by one, and thereafter the over-laid images on the intermediate transfer medium are, put together, and at once, secondary transferred onto a recording member.
This indirect transfer system has an advantage that the location for the secondary transfer can, relatively freely, be established, in comparison with for example the direct transfer system in which the toner image is transferred from photosensitive member to the recording member directly, thus sizing down of the apparatus can be designed.
Further, pursuant to the present invention, there is provided an image forming apparatus according to aforementioned image forming apparatus, wherein the toner image-receiving mean is an intermediate transfer medium, and the intermediate transfer medium is an elastic seamless belt constituted by an elastic material in the whole of it or at least one layer thereof.
In general, the color images are composed from four toners, and each toner being colored by respective own coloring agent. And one to four toner layers are formed for one color image. Pressures are given to the each toner layer in the courses of the first transfer operation to transfer the toner from the developed photosensitive member to the intermediate transfer belt, and the second transfer operation to transfer the toner on the intermediate transfer belt to the image recording sheet. Thus the aggregation force between toner particles is enhanced. The enhanced aggregation force between toner particles is apt to cause an interim void in letter image and a void induced by edge effect in solid image. In particular, the resin belts having been used hitherto possess a high hardness, accordingly does not transform pursuant to the existing toner layers, therefore is apt to compress the toner layer hence is apt to occur the inside dropout in letter image. And a requirement for forming the full-color image on various papers for instances Japanese paper or artificially embossed paper has been growing larger. However the paper having an inferior evenness surface is likely to occur the air-gaps between its surface and toner layer, hence is apt to occur an interim void caused with transfer in letter image. If increasing the transfer pressure at second transfer section for the purpose of increasing the fitness contact, it results an enhanced aggregation of toner layer, hence causes aforementioned interim void in letter image.
In the image forming apparatus of the present invention, the intermediate transfer medium is an elastic belt, the elastic belt has lower hardness in comparison with the resin belt, thus is transformed pursuant to toner layer and inferior evenness paper. Namely aforementioned elastic belt is tamed to local unevenness to transform, therefore can obtain a fitness contact without elevating the pressure for transfer the toner layer. By this feature, a transferred image having no interim void of letter image, and an excellent uniformity even if for a paper of unevenness surface can be obtain.
Further, pursuant to the present invention, there is provided an apparatus according to the aforementioned apparatus, wherein the intermediate transfer medium has a hardness(HS) by J I S(Japanese Industrial Standard)xe2x80x94A in the range 10xc2x0 to 65xc2x0.
A hardness less than 10xc2x0 of the intermediate transfer medium causes a significant difficulty to form itself with a high dimensional precision. This is caused by a nature easily influenced from shrinkage and expansion. And if wanted to be soften, an addition of oily component to the base material is a general processing, however this processing has a drawback that the oily component is oozed out by continues operation under the pressure. It becomes clear by our studies that if aforementioned oily component adhere, makes traversal strap blurring. In general, a surface layer has been provided to improve the repellency of the photosensitive member surface, but the entire prevention of the ooze out of the oily component must depend on the employment of a surface layer having high quality such as excellent durability for chemicals and the like, hence the qualification and the selection of characteristics of the material to be used becomes difficult.
On the other hand, if the hardness of the intermediate transfer medium exceeds 65xc2x0, then the increase in the hardness causes a higher dimensional precision of the formed one, and moreover, the decreased or eliminated addition of the oily component become possible. This means that the adhesion of the oily component to the photosensitive member can be decrease, however the improvements of the transfer nature such as a decrease of the interim void of letter image and so forth become impossible. And in case of a large excess hardness, thus the intermediate transfer must hardly pass over between tension rollers. In the apparatus in the present invention, the hardness of the intermediate transfer medium has the hardness ranging 10xc2x0 to 65xc2x0, therefore is no oozing out of the oily component in the continuos operation under the pressure, thus occurring no adhesion of the oily component to the photosensitive member, hence is no adhere of oily component, and makes no blurring strap in traversal direction. Further the improvements of the transfer nature such as a decrease of the interim void of letter image and so forth can be improved, and the intermediate transfer can be easily hardly passed over between the tension rollers.
Furthermore, pursuant to the present invention, there is provided an apparatus according to the aforementioned apparatus, wherein the intermediate transfer medium has a wick layer.
In case intermediate transfer medium made by an elastic belt, when the elastic belt is passed over between tension rollers, it causes an elastic deformation, thus it is easily expanded particularly to the circumference direction. The stretched intermediate transfer medium to the circumference direction causes a position shift of the colors being overlaid at the first transfer action. In the apparatus of the present invention, the wick layer in intermediate transfer medium prevents the elastic deformation of the expansion to the circumference direction, thus can accurately concords with the positions of overlaid colors, and can evade a distortion in obtained image.
Furthermore, pursuant to the present invention, there is provided a process cartridge used in image forming process, wherein the process cartridge is equipped with aforementioned electrophotographic photosensitive member.
The process cartridge of the present invention is a small abrasive of the surface of electrophotographic photosensitive member, and can prevent the generation of image drifting and image blurring for long period of use time.